Virus-glycan interactions are critical determinants of host cell invasion. Cell surface carbohydrates such as sialic acids, gangliosides or heparan sulfate are exploited by a vast number of viruses such as influenza, herpesvirus, SV40, polyomavirus, papillomavirus and other pathogens1,2. In most cases, a single class of glycans primarily serves as the cell surface attachment factor for viruses, leading to sequential or parallel engagement of other receptors/co-receptors for cell entry. Adeno-associated viruses (AAV) are helper-dependent parvoviruses that exploit heparan sulfate (HS), galactose (Gal) or sialic acids (Sia) as primary receptors for cell surface binding3,4. For instance, AAV serotypes 2 and 3b utilize HS; AAV1, 4 and 5 bind Sia with different linkage specificities; while AAV9 exploits Gal for host cell attachment. Different AAV strains also require subsequent interaction with co-receptors such as integrin αVβ5 or α5β1, fibroblast growth factor receptor (FGFR), platelet-derived growth factor receptor (PDGFR), epidermal growth factor receptor (EGFR), hepatocyte growth factor receptor (HGFR) or the laminin receptor for cellular uptake3,4.
A notable exception to the monogamous relationship between a specific AAV strain and a single class of carbohydrates is AAV serotype 6, which recognizes both Sia and HS5. However, only Sia has been shown essential for viral transduction. Structural studies have now established that the K531 residue in conjunction with R488, K528 and K533 in the VP3 subunit of the AAV6 capsid form a continuous basic patch for electrostatic recognition of HS glycosaminoglycans6-8. Similarly, the structural basis for HS recognition by AAV2 and AAV3b is well known and attributed to similar clusters of basic amino acid residues located at the three-fold axis of symmetry9-12. The Sia binding footprints for AAV1, AAV4, AAV5 and AAV6 remain to be determined. More recently, key amino acid residues involved in Gal recognition by AAV9 capsids were identified by using a combination of molecular docking and site-directed mutagenesis13. What is needed are virus vectors that have multiple glycan binding capability to exploit alternative pathways for cell entry and transduction.
The present invention overcomes previous shortcomings in the art by providing modified capsid proteins with multiple glycan binding sites, AAV vectors comprising these capsid proteins and methods for their use as therapeutic vectors.